Known compounds useful as antihypertensive agents for their human renin inhibitory activity include, for example, a compound represented by formula (III): ##STR3## wherein * indicates an asymmetric carbon atom.
Of the optical isomers of formula (III) assigned to the asymmetric carbon atom marked with * in the unit A, the one having an (R)-configuration exhibits higher activity. Therefore, it is important in the synthesis of the compound (III) to start with a compound having an asymmetric carbon atom at the position corresponding to the mark *, and it is necessary to prepare such an intermediate through asymmetric synthesis.
A known process for preparing such an intermediate having controlled asymmetry at the position * comprises acylating a lithium salt of optically active oxazolidinone with an acyl halide, diastereo-selectively alkylating the acylated compound with benzyl bromoacetate in the presence of lithium diisopropylamide (LDA), debenzylating the alkylated compound with palladium-on-carbon, and condensing the resulting compound with morpholine in the presence of diethylphosphoryl cyanide (DEPC) and triethylamine to obtain a compound represented by formula (IV): ##STR4## For details, Chem. Pharm. Bull., Vol. 38, p. 103 (1990) can be referred to. For practical application, however, this process needs an improvement in view of the insufficient yield of the alkylation.
JP-A-2-157243 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") teaches a process for preparing a compound represented by formula (V): ##STR5## by asymmetrically hydrogenating 2-(1-naphthylmethylidene)-succinic acid in the presence of a rhodium complex catalyst to obtain optically active (R)-2-(1-naphthylmethyl)succinic acid and introducing a morpholino group thereinto. However, the introduction of a morpholino group involves many reaction steps, still needing a further improvement for practical application.
Accordingly, an intermediate which can easily introduce the asymmetric moiety marked * in the unit A of the compound of formula (III) as well as a means for synthesizing the same have been keenly demanded.